2.5. Energy balance description
2.5.1. Energy consumption
The energy consumption for the membrane combined process was estimated based on the energy consumption map of a related full scale submerged MBR applied in municipal wastewater treatment [26]. In view of the flat membrane used in this study, energy consumption in the full-scale flat sheet MBR [27] was cross-referenced. The value included coarse bubble aeration or gas sparging, biological aeration, and rest MBR (influent pumping, permeate pumping, membrane cleaning, recirculation pumping, sludge disposal and controls). Furthermore, the expenditure for a conventional MBR treatment system for municipal wastewater was also listed for comparison.
Considering the intermittent use of the dual membrane system, the energy consumption for synthetic wastewater up-concentration was calculated in accordance with the actual operating time.
2.5.2. Energy recovery from methane
Combined heat and power (CHP) technology is a promising approach to increase energy capture at WWTPs with anaerobic digesters [3]. In this study, microturbine-based CHP technology was selected to analyze energy recovery from methane because it can run on biogas to produce power energy. Assuming a power energy efficiency of about 40%, energy recovery from methane was calculated by applying the following theoretical equation (Eq. (3)) [28]:
equation(3)